1. Field of the Invention
The subject invention generally pertains to electric motors and more specifically to a device for protecting a motor's bearings from moisture contamination.
2. Description of Related Art
The motors of some vacuum cleaners, particularly water extractor appliances such as carpet cleaners and wet/dry vacuums, are exposed to a significant amount of moisture-laden air. To protect the motor's bearing from being damaged by the moisture, a seal can be installed between the bearing's inner and outer races or somewhere between the motor's rotating shaft and the motor's stationary housing. As the motor turns, such seals rub against a sealing surface, which can eventually wear out the seal or wear out the surface against which the seal rubs.
Nonetheless, such rubbing style seals can have an acceptably long life when applied to induction motors that run at 1800 rpm or some other relatively low speed tied to the line frequency of the motor's supply current.
Lightweight vacuum cleaners and other portable appliances, on the other hand, preferably have a more lightweight motor, such as a universal or series motor. The rotational speed of universal motors are not limited by the frequency of the motor's electric supply, so they may run at over 20,000 rpm. Thus, rubbing style seals for universal motors may need exceptionally high wear resistance (both the seal itself and the surface against which it rubs). Moreover, universal motors need to me manufactured to very close tolerances to run at such high speeds.
Consequently, seals for universal motors preferably have high wear resistance, sufficient flexibility to provide a shape conforming seal, sufficient rigidity to meet the motor's tolerance requirements, and low coefficient of friction to avoid generating heat. It can be difficult, however, to provide a single seal having all of those qualities.